1. Field of the Invention
The present invention relates to a silver halide photographic emulsion with a high sensitivity and sharpness and improved dependence on processing.
2. Description of the Related Art
Recently, compact cameras provided with a zoom lens are increasing, and compact zoom cameras with high zoom ratios, such as 3:1 and 4:1, are becoming the mainstream. These zoom cameras are not always satisfactory in respect of image quality, although they are useful for readily taking pictures. For example, in some types of such cameras the f-number of the lens exceeds 10 when the lens has been shifted to the telephoto side, which tends to cause under-exposure. Further, the strobe range of compact cameras is short, and in many cases under-exposure occurs. A film with a high sensitivity which can improve such a situation is desired.
In 1996, Advanced Photo System (APS) cameras having a smaller picture size on the film than the conventional 135 format were put on the market. Since the film-print enlarging ratio of the APS format is greater than that of the conventional 135 format, APS requires films of a higher image quality.
To meet such demands, development of tabular silver halide grains have been made in order to increase photographic sensitivity and reduce the grain size. Methods of manufacturing tabular silver halide grains and techniques of use thereof have already been disclosed in U.S. Pat. Nos. 4,434,226, 4,439,520, 4,414,310, 4,433,048, 4,414,306, and 4,459,353, etc. These documents disclose the advantages of tabular silver halide grains, such as improvement in the relationship between sensitivity and graininess, including improvement in color sensitization efficiency by using spectral sensitizing dyes.
However, when the aspect ratio (grain equivalent circle diameter/grain thickness) of each grain is increased to pursue the advantages of tabular grains, the grain thickness is reduced. In particular, a photosensitive material using grains each having a thickness of less than 0.13 μm and an equivalent-circle diameter of 1.0 μm or more proved to be inferior in processing stability, and could not be put to practical use. Therefore, it was impossible to use very thin tabular grains, each having a thickness of less than 0.13 μm, for films with a high image quality and high sensitivity.